Interconversion of alcohols, aldehydes, and ketones are essential processes in both prokaryotes and eukaryotes. The oxidoreductases catalyzing these reactions use a variety of different electron acceptors and can be divided into three main groups: 1. the NAD(P)-dependent alcohol dehydrogenases 2. the NAD(P)-independent alcohol dehydrogenases, which use other cofactors for catalysis; and 3. FAD-dependent alcohol oxidases, which catalyze irreversible oxidation of alcohols. H Thermoanaerobacter (formerly Thermoanaerobium) brockii alcohol Hdehydrogenase (TBADH) is a medium chain, NADP-linked, class A enzyme Hthat reversibly catalyses the oxidation of secondary alcohols to the Hcorresponding ketones. H The ubiquitous alcohol dehydrogenases (ADHs) are found not only Hin bacteria, but also in yeast, plants, insects and in man. ADH is an oxidoreductase, requiring either NAD(H) or NADP(H) as a coenzyme, that reacts with primary and secondary, linear and branched-chain, aliphatic and aromatic alcohols and with their corresponding aldehydes and ketones. Although some ADHs depend on iron for activation and certain ADHs are known to be metal-free, most ADHs contain zinc at the Hactive site. Zinc-dependent ADHs are either dimers, usually found in Hhigher plants and mammals, or tetramers, such as those present in Hyeast and bacteria. A monomeric ADH was isolated from Saccharomyces Hcerevisiae, but its metal content is yet unknown.